In U.S. Pat. No. 4,059,300 there is disclosed a seal formed of plastic, comprising a housing open at the front end and closed at the rear end, with internal resilient fingers extending from the rear end, and a shackle carrying a stud on the remote end which is shaped and dimensioned for nonremovable engagement with the fingers. To assist in preventing access to the fingers and preventing release of the stud from the housing by forcing the stud laterally in the housing to effect release of the fingers with a suitable pick, a separate plastic piece in the form of a collar is assembled into the housing. The seal is manufactured by injection molding the housing, resilient fingers, shackle, and stud as a single piece of material with both ends of the housing being open in the as molded condition, assembling the plastic collar into the rear end of the housing, and then closing the rear end into a dome-shaped configuration by heated dies.
Although the seal disclosed and claimed in said patent has achieved considerable commercial success and is used in many applications, it has been found difficult to reliably close the rear end of the housing in high speed volume production. Also, such closing operation can leave a visible ring around the rear end of the housing which can obscure a cut made on this line by an unauthorized person tampering with the seal.
Also, the dimensions of the locking fingers must be very accurate to insure proper locking of the stud into the fingers, however the required dimensions of the fingers are difficult to maintain in the molding operation, since the fingers are at the end of the shackle, and therefore part of a much larger piece of plastic.